Isotopes have innumerable medical, industrial and scientific applications. In particular, for various nuclear applications, it is important to be able to separate the fissile isotope .sup.235 U from, or to strongly enrich .sup.235 U in admixtures with, other isotopes of uranium.
For many years, gaseous diffusion has been the only process by which .sup.235 U isotope enrichment and separation has been carried out. Gaseous diffusion plants are large and expensive operations which, although clearly operational, leave much to be desired by way of efficiency.
Very recently, a most promising solution has come with the advent of high output lasers, and in particular, high output lasers which operate in the infrared portion of the electromagnetic spectrum, such as CO.sub.2 lasers.
It is known that by controlling the spectral frequency of the light interacting with matter it is possible to produce selective reactions that can change the composition and properties of the matter. The conditions required to achieve such selectivity are (1) high monochromaticity of the exciting light; and (2) the selectivity of the primary process of light interaction with the matter (the existence of narrow nonoverlapping absorption lines). See, e.g., R. V. Ambartzumian and V. S. Letokhov, "Selective Two-Step (STS) Photoionization of Atoms and Photodissociation of Molecules by Laser Radiation," 11 Applied Optics 354 (1972), V. S. Letokhov, "Use of Lasers to Control Selective Chemical Reactions," 180 Science 451 (1973), and A. Ashkin, "The Pressure of Laser Light," Scientific American, March (1972).
The first condition can readily be met by lasers. The art discloses that the second condition presents substantial difficulties but can be achieved provided there exist certain discrete electronic and vibrational transitions of the matter in the gaseous phase. As a practical matter, it is frequently difficult to ascertain in a gaseous species which transitions are appropriate for selective interaction with tuned laser light.
The literature, however, discloses how this particular problem can, in principle, be readily overcome. It is known that if molecules containing a mixture of isotopic species of a particular element are irradiated with laser light tuned to excite molecules containing only a particular isotopic species of the element, only those molecules containing that particular isotopic species will be excited by the laser light, and that such excited molecules will move in the direction that the photon absorbed was moving, because of the absorbed momentum of the photon. It is also well known that molecules so excited can be stimulated to emit a photon by another photon-molecule interaction and that a molecule undergoing stimulated emission moves in a direction opposite to the direction the emitted photon moves. The molecule will emit a photon when stimulated, in the direction the stimulated photon was moving before collision with the molecule.
The apparatus and method of the instant invention essentially depend on these physical steps in carrying out the invention.